Method of constructing lightweight antenna



May 7, 1968 E. D. RUSSELL METHOD OF CONSTRUCTING LIGHTWEIGHT ANTENNA 2 Sheets-Sheet 1 Filed Sept. 27, 1965 Earl D. Russell ATTORNEY y 7, 1968 E. D. RUSSELL 3,381,371

METHOD OF CONSTRUCTING LIGHTWEIGHT ANTENNA Filed Sept. 27, 1965 2 Sheets-Sheet 2 Figure 4A Earl D, Russell INVENTOR BY M D/M ATTORNEY United States Patent METHOD OF CONSTRUCTING LIGHTWEIGHT This invention relates to an improved method of constructing an antenna and is a continuation in part of my earlier filed application Ser. No. 160,451, entitled Lightweight Spiral Antenna, filed Dec. 19, 1961, now abandoned. More specifically, it relates to a method of constructing an antenna having a strip-like radiating element spaced from a reflecting surface that is formed on a dielectric support. The support is cast of a foam material and painted with a conducting paint to form the reflecting surface. The construction is substantially simpler than prior techniques and provides a lightweight antenna readily fabricated at low cost.

Antennas often have conducting surfaces spaced behind the radiating elements to reflect signals and thus form directional radiation patterns. Prior antenna constructions of this type require rigid, self-supporting reflectors, fabricated from sheet metal or castings, and, accordingly, they are heavy and bulky. In addition, the prior constructions are costly, since they require several fabricating operations. Furthermore, relatively bulky fastening devices are required to secure the heavy reflector to the assembly.

Accordingly, it is a principal object of the present invention to provide an improved method of constructing an antenna having a reflecting surface spaced from the radiating element.

A more specific object is to provide a method of constructing a directional antenna having a substantially plane radiating element, that is substantially less costly and light in weight than prior antennas of this type.

Other objects of the invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the several steps and the relation of one or more of such steps with respect to each of the others to form the article possessing the features, properties and the relation of elements, which are exemplified in the following detailed disclosure, and the scope of the invention will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawings, in which:

FIGURE 1 is a top plan view partly broken away of an antenna constructed in accordance with the present invention.

FIGURE 2 is a sectional view taken on the line 2-2 of FIGURE 1,

FIGURE 3 is a sectional view similar to FIGURE 2, of another embodiment of an antenna constructed in accordance with the present invention,

FIGURE 4 is a sectional view of a mold utilized in the construction of the antenna shown in FIGURES 1 and 2, and

FIGURE 4A is an enlarged portion of a section of the mold shown in FIGURE 4, illustrating the various layers of materials utilized in the present invention.

In general, the present antenna construction features a rigid, light-weight insulator that is painted with a conducting film and mounted behind a radiating element. The film reflects signals so that the antenna radiates a directional pattern.

3,381,371 Patented May 7, 1968 ice The insulator is preferably a foamed material, cast in a mold which is coated with the conducting film and secured to the radiating element. When the mold is removed, the film adheres to the hardened insulator. In this manner, the reflector is fabricated in the desired shape and secured to the radiating element in a single operation to provide a low-cost, light-weight antenna.

Referring to FIGS. 1 and 2, the antenna has a substantially flat radiating element 10, such as a double Archimedean spiral, energized by means of a coaxial feed cable 12 having a conductor connected to each of the spirals 10a and 10b. A reflector 14 is supported by a substantially rigid insulator 16 secured to a dielectric board or sheet 18, to which the spirals: 10a and 1% are bonded. A conducting sleeve 20 ensures a good electrical connection between the reflector 14 and the outer condoctor 12a of the cable 12.

The insulator 16, preferably a cylinder made of lightweight dielectric foam, effectively supports the reflector 14 at the desired distance from the radiating element 10, so that the antenna radiates in a predetermined directional pattern.

The antenna is preferably constructed by forming the Archimedean spirals 10a and 10b of thin high-conductivity metal on one or both sides of the dielectric board 18, using, for example, printed circuit techniques. The radiating element can also be an equiangular element or other type of broad band radiator of which log periodic is a type.

The feed cable 12 is then connected to the radiating element through a hole 18a (FIG. 2) formed in the board 18. With the double Archimedean spiral shown, the coaxial inner conductor 12b is connected to the spiral 10a, and the outer conductor 12a is connected to the spiral 101;. It is apparent that a waveguide or strip transmission line feed system can be used instead of the coaxial line shown.

The insulator 16 is preferably made of a dielectric foam cast in a mold 11 (FIG. 4) having a cavity 13 with the desired shape for the insulator and an aperture 15 for the cable 12. The mold is coated with a mold release agent 17 and then with a conducting paint 19 such as a silver-epoxy. The cable 12 is then secured to the board 18 and the latter is secured to the mold, e.g., by clamps, and the insulator 16 foamed in place according to wellknown techniques, for example, by adding a suitable catalyst to the dielectric material before closing the mold. The material preferably has a low dielectric constant and forms a unicellular foam. A suitable material is phenolic or epoxy foam. As the foam hardens, it adheres to the conducting paint, which serves as the reflector 14. It also adheres to the board 18 to form a unitary structure of the entire assembly. The feed cable 12 may be anchored within the insulator, as shown, prior to foaming of the insulator 16.

The aperture that accommodates the conducting sleeve 20 may be molded in place or formed after the mold has been removed. The assembly of the antenna is then completed by securing the sleeve in place. Alternatively, the sleeve 20 may be inserted into the mold after the release agent is applied and before the application of the conducting paint, as shown in FIGS. 4 and 4A. The paint then adheres to the sleeve to form an efficient connection thereto. A suitable coating, indicated by the dashed line 21, may be applied to protect the reflector 14 after the unit is removed from the mold.

As shown in FIGS. 1 and 2, the insulator 16 is preferably a solid right cylinder, and the electrical distance between the element 10 and the reflector portion 14a parallel to the element, is preferably a quarter-wavelength at the geometric mean of the design frequency. This spacing generally provides the optimum combination of antenna radiation pattern and impedance. The connection between the feed cable outer conductor 12a and the reflector 14 maintains the reflector at substantially ground potential.

Using the foregoing process, the antenna can be con structed with low-cost materials, and its size and weight are substantially reduced as compared to similar antennas constructed according to prior techniques. For example, .an S-band antenna, operating between 2 and 4 kmc., is 80% lighter than a similar prior antenna having a cast aluminum reflector.

In addition, the reflector 14 is fabricated and secured in place in substantially a single process, whereas the prior construction required the machining of a casting and securing it to the dielectric board 18.

Referring now to FIG. 3, according to an alternative construction, the reflector 14 is formed on a can-shaped insulator 22 secured with suitable adhesive 23 to the dielectric board 18. A conducting fillet 24 of solder or the like connects the reflector 14 to the feed cable outer conductor 12a.

More specifically, the insulator 22 is preferably cast in the desired shape using, for example, a phenolic material. The reflector 14 may be formed on either the inside or the outside of the insulator by painting the insulator or a mold, which is not shown but which is similar to mold 11, with a silver or other conducting epoxy. The feed cable 12 is then fed through the insulator 22 and secured to the radiating elements 10a and 10!) by soldering, for example. The adhesive 23, a low-loss epoxy or other cement, fastens the dielectric board 18 to the support and the conducting fillet 24 is then formed between the outer conductor 12a and the reflector 14. A protective film, shown dotted at 26, is preferably sprayed over the reflector 14 on the outside of the insulator 22.

The intenna constructed with the hollow cylindrical insulator 22 is even lighter than the antenna described above with reference to FIGS. 1 and 2, in addition to retaining its small size and low cost. It will be apparent that the radiating element and associated surface of the dielectric board may have a surface shape other than planar. For example, the surface may be conical with the apex of the cone pointing away from the reflector.

It will thus be seen that the objects set forth above,

among those made apparent from the preceding description, are efficiently attained and, since certain changes may be made in carrying out the above method and in the constructions set forth without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

Having described my invention, what I claim as new and desire to secure by Letters Patent is:

What is claimed is:

1. A process for constructing an antenna having a radiating clement, said process comprising the steps of securing said radiating element to a dielectric board, securing to said dielectric board a dielectric support projecting substantially transverse to the plane thereof by casting a dielectric foam in a mold having a cavity closed by said dielectric board, and forming a thin conductor on said dielectric support to reflect electromagnetic signals radiated by said element.

2. A process for constructing an antenna comprising the steps of fabricating a strip-like radiating element on a dielectric sheet, electrically connecting a feed system to said radiating element, coating a mold cavity having a substantially cylindrical configuration with a release agent and then with a conducting epoxy, closing said cavity with said sheet, said feed system extending axially through said cavity, casting a solid cylinder of dielectric foam in said mold cavity and permitting the same to harden therein, whereby said hardened foam adheres to said dielectric sheet and said epoxy, removing said cylinder from said mold cavity, and connecting said epoxy to a conductor of said feed system.

References Cited UNITED STATES PATENTS 2,863,145 12/ 1958 Turner 343-895 X 3,049,711 8/1962 Hooper 34389 X 3,131,394 4/1964 Wheeler 343-895 3,143,770 8/1964 Jeske 26445 X 3,169,311 2/1965 Small et al 343-912 X CHARLIE T. MOON, Primary Examiner.

R. W. CHURCH, Assistant Examiner. 

1. A PROCESS FOR CONSTRUCTING AN ANTENNA HAVING A RADIATING ELEMENT, SAID PROCESS COMPRISING THE STEPS OF SECURING SAID RADIATING ELEMENT TO A DIELECTRIC BOARD, SECURING TO SAID DIELECTRIC BOARD A DIELECTRIC SUPPORT PROJECTING SUBSTANTIALLY TRANSVERSE TO THE PLANE THEREOF BY CASTING A DIELECTRIC FOAM IN A MOLD HAVING A CAVITY CLOSED BY SAID DIELECTRIC BOARD, AND FORMING A THIN CONDUCTOR ON SAID DIELECTRIC SUPPORT TO REFLECT ELECTROMAGNETIC SIGNALS RADIATED BY SAID ELEMENT. 